This guide assumes there is no Internet, no Wifi, no router, no display, no keyboard. It assumes you have a Raspberry Pi and laptop with:
- Ethernet port (built-in or USB-Ethernet adapter)
- plain (or crossover) Ethernet cable–no router/switch is required
Some laptops can also work via USB-C connection and the RNDIS Ethernet driver instead of the Ethernet jack. However, some laptops, particularly on Windows may not work for RNDIS. The symptom of this is that the Pi shows up as a serial port instead of an Ethernet connection. Hence, best to use the Ethernet jack for better reliability.
Before going into the field away from internet, download:
Prepare SD card via the Raspberry Pi Imaging tool to write the desired SD card image. If the laptop is not on the internet, use the imager tool to write the .img you downloaded previously. BEFORE writing, use Imager settings to enable SSH, set username, hostname, etc.
“eject” or unmount the SD card before removal, to avoid corrupting the SD card file system.
Boot the headless Pi by inserting the SD card into the Pi and powering up the Pi.
We use link-local networking, where the IP address will be in the
169.254.*.* range, no DHCP server needed.
You may need to manually select this network when you plug the Pi into your laptop.
After about one minute, on your laptop plugged directly to the Pi via Ethernet (username, hostname are those picked for the Pi by the Raspberry Pi Imager program):
Just a simple network switch connecting Raspberry Pis, PCs and other devices makes an internet-free, pure link-local “off the grid” network.
Of course, you can also put the Pis on a wired or wireless network connected to the Internet if desired.
.local address functionality will NOT work over the Internet, but only on the LAN segment your device is on.
Without further configuration, SSH servers listen on all interfaces.
Normally this is fine.
If you want only specific interface(s) to have the SSH server listen, you will need to research
/etc/ssh/sshd_config and/or IPTables.